Such vacuum pumps can be used to evacuate a process chamber, through which hazardous/aggressive process gases may be passed to perform various functions in use. Dry vacuum pumps typically comprise one or more oil filled gear boxes. These are generally located remotely from the pump swept volume within the pumping apparatus. The swept volume accommodates the pumping mechanism which, in turn, is attached to and driven by the gear box, via one or more rotating shafts. It is important to prevent the transfer of oil from the gear box to the swept volume as oil would contaminate the process gases and potentially migrate to the process chamber, causing damage to the article being processed. It is also important to prevent particulate matter from the swept volume from reaching the gear box as this may cause contamination of the gear box oil and, consequently, reduce the reliability of the gear box components.
Conventionally, rotary seals are used around the rotating shafts to prevent transfer of oil from the gear box. However, it is very difficult to produce rotary seals which are suitably reliable and hardwearing. In trying to achieve these goals, exceptionally complex and expensive seals have conventionally been developed.
Loss of oil from the gear box not only causes potential contamination, but leads to degradation of the gear box itself if the volume of oil is significantly reduced. One conventional system collects such migrating oil but regular maintenance must be carried out to replenish the levels in the gear box and to empty the oil collection chambers.
It is an aim of the present invention to increase the maintenance interval by providing a system that prevents or significantly reduces the loss of oil from the pump.